1. Field of the Invention
This invention relates to a signal processing circuit used in detecting peaks of pulse signals read out from a magnetic head of a hard disk device.
2. Description of the related art
Many methods exist for removing pseudo peaks--which arise from noise, for example--from a read-out signal output via the magnetic head of a hard disk device. Typical pseudo peak removal methods are the time domain system, the level-slice system, the minute voltage system, also called the .DELTA. (delta) V system, and the like. In the case of the .DELTA.V system, for example, the true peak level of an original waveform is used as a reference level, with those peaks below the reference level being treated as pseudo peaks and therefore removed. Because this system is free from the problem of the amplitude limit of the original waveform, it has, accordingly, found widespread application, from MFM modulation to RLL modulation.
When using the .DELTA.V system, the peak position of the read-out signal from the magnetic head must be delayed a predetermined period of time; conventionally, the read-out signal is subjected to the delay processing in the analog signal mode.
A prior signal processing circuit based on the .DELTA.V system, is shown in FIG. 1, while signal waveforms at key points in this circuit are shown in FIG. 2. A read-out signal A from the magnetic head is delayed a predetermined time of period by analog delay circuit 61, which includes an LCR type filter. Signal A then becomes delayed signal B which, in turn, is differentiated by differentiator circuit 62. The resulting differentiated signal C is then supplied to comparator 63, where it is converted into a digital signal D. Finally, signal E corresponding to the write data is reproduced by use of digital signal D.
Using an analog circuit for signal delay presents the following problems:
In order to expand the frequency range in which the signal can be read out, it is necessary to provide a large number of filters in the signal processing circuit. When a large number of filters is provided in the signal processing circuit, it is necessary to provide a large number of external LCR elements on the wiring board, leading to the signal processing circuit of undesirably large size.
As is clear from the above, in the signal processing circuit based on the .DELTA.V system for pseudo peak removal, the entire circuitry cannot be fabricated into a circuit with a high packing density. This creates many problems, such as higher manufacturing costs, a large number of required external elements, a large chip area occupied by the signal processing circuit, and difficultly in design work of the circuit.